This disclosure relates to controlling the position of a moving light fixture.
Full positional feedback is important for moving light fixtures. Moving light fixtures are often propelled by either DC servo motors or stepper motors. DC servo motors provide full positional feedback. However, DC servo motors are extremely expensive and cost prohibitive for new product development. Stepper motors are relative position devices that require a known reference position. The pan and tilt axes in a moving light fixture with stepper motors typically requires homing to a known position on start-up. This homing operation takes time to complete and requires that the moving light fixture has full, unencumbered movement. It precludes operating the moving light fixture on a tightly packed lighting bar, directing the moving light fixture through a window or aperture, or otherwise operating the moving light fixture with a restricted range of movement. The homing operation also produces an undesirable noise in theatrical environments, especially if re-homing needs to occur during a live production.
Some conventional moving light fixtures with stepper motors address this issue using optical quadrature encoders. However, optical quadrature encoders provide only relative positional feedback, not absolute. In addition, optical encoders allow a moving light fixture with stepper motors to correct its position while in use, but does not provide an immediate known position upon power up. Thus, a homing operation is still required.
Other conventional moving light fixtures address this issue using full resolution rotational absolute position sensors. However, sensors of this type that provide the resolution required for moving light fixtures are prohibitively expensive.